commit a790fb8873f1cbe8b9cb48cb368851e30d3ec172
Author: Patrick McHardy <kaber@trash.net>
Date:   Tue Jul 14 10:19:47 2009 +0200

    net-sched: sch_cbq: fix locking in cbq_undelay()
    
    The hrtimer callback cbq_undelay() is not serialized against
    cbq_ovl_delay(). That affects at least q->pmask and q->delay_timer.
    
    Lock it proper.
    
    Based on patch by Thomas Gleixner <tglx@linutronix.de>
    
    Signed-off-by: Patrick McHardy <kaber@trash.net>

diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 23a1676..7c659c6 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -593,12 +593,16 @@ static enum hrtimer_restart cbq_undelay(struct hrtimer *timer)
 	struct cbq_sched_data *q = container_of(timer, struct cbq_sched_data,
 						delay_timer);
 	struct Qdisc *sch = q->watchdog.qdisc;
+	spinlock_t *root_lock;
 	psched_time_t now;
 	psched_tdiff_t delay = 0;
 	unsigned pmask;
 
 	now = psched_get_time();
 
+	root_lock = qdisc_lock(qdisc_root(sch));
+	spin_lock(root_lock);
+
 	pmask = q->pmask;
 	q->pmask = 0;
 
@@ -615,6 +619,7 @@ static enum hrtimer_restart cbq_undelay(struct hrtimer *timer)
 				delay = tmp;
 		}
 	}
+	spin_unlock(root_lock);
 
 	if (delay) {
 		ktime_t time;